Vegetable production - trap crops valuable tools

The No. 1 problem in vegetable production in the Southeastern United States is insect pests, according to Ayanava Majumdar, Auburn University Extension entomologist and the state coordinator for Sustainable Agriculture Research and Education.

Caterpillar pests of vegetables have long been the major issue for vegetable producers, he says, including diamondback moths, squash vine borers, hornworms and armyworms. “Those insects can cause 100-percent crop loss if control measures are not taken. Sucking insect pests such as stink bugs and leaf-footed bugs also are emerging problems in vegetable production. Stink bugs typically become a problem in mid- to late-season and heavy infestations may cause fruit and flower drop, affecting plant yield, says Majumdar.

It can be difficult, he says, to manage caterpillars and stink bugs with currently available general-use pesticides that may give rise to insecticide resistance and cause non-target effects. “An alternative method to combat insect pests is by the use of trap crops,” says the entomologist.

A trap crop is an attractive host plant that attracts insects away from the main crop during a critical time period. “The basic principle of trap cropping is that insects have a preference for host plants and will move to a preferred host if given a choice. Insects are highly attracted to reproductive stages of host plants over the vegetative stages and trap cropping uses this attraction to good use,” he explains.

Generally, the trap crop is considered “sacrificial” because it protects the valuable main crop when pest populations exceed normal levels. The target insect must be controlled in the trap crop with timely insecticidal applications or by mechanical removal.

Since the 1930s, says Majumdar, there have been many reported cases of successful trap cropping for management of various insect pests resulting in great reduction in the use of pesticides.

“The benefits of trap cropping include reduced dependence on insecticides, the low cost of trap crop seed, conservation of natural enemies, and better crop and environmental quality. But remember, trap cropping is not a silver bullet solution to all of our pest problems because it does require more pest management skills and the knowledge of insect behavior. Also, not all insects can be controlled with trap crops,” he says.

There are two ways you can use trap cropping, says Majumdar. One may be to use the same plant cultivar as a main crop and a trap crop. The trap crop is planted much earlier than the main crop in order to serve as food for the insects.

Completely different species

“The main crop and trap crop are entirely different species. Research has shown that hot cherry peppers trap crop can protect bell peppers by reducing damage from many insects, including pepper maggots. Early planted tomatoes can serve as trap crops for the multiple pests to protect a patch of desirable tomatoes,” he says.

Blue hubbard squash or other susceptible varieties can be used as a trap crop to attract and retain cucumber beetles, squash vine borers and squash bugs, says Majumdar.

“Some trap crops for stink bug management include buckwheat, okra, green bean, sunflower and sorghum. These trap crop seeds are inexpensive and readily available at local feed-and-seed stores. Sunflower appears to be attractive to leaf-footed bugs as well, but it has to be planted very early in order to be blooming by the time the bugs begin to migrate in high numbers.”

Trap cropping is management intensive because insects must be removed manually (e.g., by hand-collection and drowning) or killed with insecticides (synthetic or biological formulations) as soon as the bugs appear in low numbers, says Majumdar.

Scout the trap crop continuously, he advises, and do not wait for the populations to increase over time. If the bugs are not controlled early, then this strategy will backfire and cause more problems because the traps crop will then serve as a “nursery crop.”

Past research on caterpillars suggests that no more than 20 percent of the total production area in a field may be dedicated to trap cropping in order to be economically justified. Trap crops should always be planted on good ground so they remain healthy and attractive to the target pests.

“Trap crops can be arranged in various spatial patterns and the choice of design will depend on target pest, pest pressures and farm size. Extremely mobile insects such as cucumber beetles are more difficult to manage with trap cropping than the slow moving insects like the Colorado potato beetle.”

Some of the spatial arrangements include perimeter trap cropping (PTC), row trap cropping (RTC) and strip trap cropping (STC), he says. By far, PTC is the most popular trap cropping arrangement used by farmers. Perimeter trap crops can be planted on four sides of the main crop in sufficient density in order to provide a physical barrier to mobile insects.

For example, sorghum and sunflower can be effective as PTC when planted in two to three wide rows. The developing heads of those trap crops may get covered with stink bugs.

RTC is a type of inter-cropping where rows of trap crops alternate with several rows of the main crop. Buckwheat can be planted as a row trap crop for stink bug control. Buckwheat (densely planted) is also suitable for sheltering natural enemies and pollinators.